1. Field of the Invention
The present invention relates to a lining for protecting the interior of a metallurgical vessel which is intended to contain a molten metal such as liquid steel.
The invention is also directed to a method for forming a protective internal lining of this type.
The metallurgical vessel which it is desired to protect by means of an internal lining in accordance with the invention can be a casting ladle, a tundish or a slag vessel.
2. Description of the Prior Art
A metallurgical vessel of the type mentioned in the foregoing usually has an outer shell of steel provided with a lining of refractory material such as bricks of magnesia, alumina or aluminosilicate or of refractory cement.
At the end of the casting operation, it is necessary to remove the residues remaining within vessels which have contained the molten metal. These residues have a highly corrosive action on the lining of refractory material, with the result that the lining becomes worn in the course of time and has to be replaced at the end of a limited period of use. This replacement operation, however, is both complicated and costly.
Many solutions have already been proposed for providing the permanent refractory lining of metallurgical vessels with protection against corrosive wear.
French Pat. No. 2,316,027 advocates the protection of all the internal portions of a vessel or ladle for transfer of molten metals by interposing sinterable elements between the permanent refractory lining and the molten metal, these elements being usually provided in the form of plates.
French Pat. No. 2,393,637 describes a similar protection provided with or without the aid of prefabricated refractory insulating elements which are sinterable in contact with liquid steel, said elements being bonded to the permanent refractory lining by application of a composition which is substantially identical with that of the prefabricated elements aforesaid.
In French Pat. No. 2,451,789, the permanent refractory lining of a metallurgical vessel is protected by means of a relatively compressible layer between said permanent refractory lining and an internal lining which comes into contact with the liquid steel, said compressible layer being formed by a base of organic and/or inorganic fibers coated with a binder.
Another solution advocated in German Federal Republic patent application No. 2,010,743 consists in incorporating non-agglomerated sand beneath the prefabricated elements and behind these latter in order to increase the heat-insulation coefficient of the wearing lining which comes into contact with the liquid steel.
French Pat. No. 2,393,637 already cited in the foregoing also describes the possibility of applying, projecting or introducing the composition by means of a mold which leaves a uniform internal space between the mold and the wall to be lined, the composition being introduced into said uniform space by tamping and/or blowing, by suction or by vibration.
All these solutions are attended by many disadvantages.
Protective internal linings consisting of plates or prefabricated elements are relatively costly and complicated to instal. Furthermore, these plates or prefabricated elements do not usually afford resistance to more than five of six successive casting operations.
In order to avoid any hydrogen contamination of molten metal, it is necessary in some instances to preheat protective lining plates to a temperature above 600.degree. C. in order to eliminate moisture as well as the organic compounds contained therein.
During the preheating process, the plates or prefabricated elements exhibit a tendency to buckle under the action of heat, thus forming gaps between the joints of said plates or elements, with the result that the molten metal is liable to seep through the gaps and thus to reach the permanent refractory lining.
This situation becomes even worse when the gap formed between the plates and the permanent refractory lining is filled with powdery material such as sand. In fact, this powdery material is liable to contaminate the molten metal as it flows through the gaps formed between the plates which have buckled under the action of heat. Furthermore, by seeping through these gaps, the molten metal mixes with the powdery material and thus forms a mass which strongly adheres to the permanent refractory lining, with the result that this permanent lining then becomes very difficult to clean.
The single-layer internal linings formed by projection of spray-coating as described in French Pat. No. 2,393,637 and obtained from a mixture of refractory inorganic particles and of an inorganic or organic binder are not attended by the above-mentioned disadvantages of plates or other prefabricated elements.
Internal linings of this type must necessarily sinter in contact with the molten metal in order to guard against any danger of detachment of inorganic particles from these internal linings since such particles would cause contamination of the molten metal.
The sintering process just mentioned takes place progressively and, after a certain period of contact between the molten metal and the protective internal lining, the entire mass of said lining is sintered, thus giving rise to the following two drawbacks:
in the first place, when the entire mass of the protective internal lining is sintered, this lining has appreciably lower heat-insulating power, with the result that there is a potential danger of cooling of the molten metal; PA0 in the second place, when the entire mass of the internal lining has sintered, this mass adheres to the permanent refractory lining and this latter then becomes very difficult to clean. PA0 a layer having a composition and granular size of refractory inorganic particles which are such that said layer sinters throughout its mass under the action of the heat of the molten metal contained in the metallurgical vessel; PA0 a layer having a composition and granular size of refractory inorganic particles which are such that said layer does not sinter or sinters only to a partial extent in order to remain friable even when the first layer has completely sintered.
For the two reasons just given, sintering of the protective internal lining is not allowed to proceed to completion. Thus, when the casting operation is completed, said internal lining can be detached in one piece from the internal walls of the metallurgical vessel simply by overturning the vessel.
In consequence, said protective lining can be used only for a few successive casting operations and therefore has to be replaced at frequent intervals. Each replacement is relatively costly and causes an interruption of the casting operation, which is also unfavorable from an economic standpoint.
In French Pat. No. 2,338,100, it has been proposed to place between the sinterable internal lining and the permanent refractory lining a material having a paper base, for example, in order to provide the possibility of limiting the risks of adhesion between the sintered internal lining and the permanent refractory lining. However, this material chars rapidly under the action of heat and is consequently incapable in practice of performing the function just mentioned.
The aim of the present invention is to overcome the disadvantages of the known solutions discussed in the foregoing by providing a protective internal lining which is both inexpensive, easy to instal, affords resistance to a large number of successive casting operations, withstands high preheating temperatures without damage, makes it possible to maintain a high heat-insulating power during a large number of successive casting operations, and effectively guards against any risk of adhesion between the protective internal lining and the wall of the metallurgical vessel, with the result that cleaning of the vessel on completion of the casting operation is considerably facilitated.